High dielectric material and method of making same



Patented June 18, 1946 UNITED STATES PATENT OFFICE HIGH DIELECTRIC MATERIAL AND METHOD OF MAKING SAME No Drawing. Application June 11, 1943, Serial No. 490,485

7 Claims. 1

The present invention relates to ceramic dielectric materials and to methods of making the same. More particularly, the invention relates to such materials in which compounds of titania a the predominating constituent are used in combination with compounds of tin.

In copending applications for patent, Ser. No. 465,387, filed November 12, 1942 and Ser. No. 482,613, filed April 10, 1943, the useful properties of barium titanate-strontium titanate mixtures are described. The present invention relates to another group of bodies whose usefulness is equally widespread. in that this group of ceramic compositions has properties such as to make them useful as capacitors in radio, television and communications generally, as capacitative temperature compensating devices in receivers and communication equipment to prevent distortions due to changes in circuit characteristics caused by temperature changes. The dielectric constants of some of these compositions are so high that their utilization in low frequency distribution and communication systems such as 60 cycle lines, by means of capacitative coupling between a low frequenc (20 to 120 cycle) high tension transmission line and communication telephone line, is made possible.

Further, the very high dielectric constants of the ceramic composition of the present invention make possible the use of these materials as electro-mechanical devices, for example the transfer of mechanical energy or motion into electrical energy or vice versa, in a fashion similar to the action exhibited by piezoelectric crystals. Thus my novel compositions have possible utility in piezoelectricity, supersonics, crystal or condenser microphones, frequency stabilizers. loud speakers, phonograph pickups, telephone design, and oscillator designs generally. The foregoing remarks apply particularly to those bodies whose dielectric constants are over 1000 at radio frequency. In condenser microphones, very thin sheets of the higher dielectric constant materials are rigidly clamped at either the center or edges and used as the vibrating diaphragm. The minute changes of position or dimension of the dielectric due to vibration will occasion relatively large changes in capacity by means of which sound is transformed into electrical energy.

Other members of this group, particularly those having dielectric constants over 1000 exhibit electrical and mechanical characteristics of the same nature as piezoelcctrical and pyroelectrical crystals. For example, a rod of the material havin one end fixed and one end free to vibrate will when in vibration, develop a potential difierence of several volts between the two ends of the rod.

The particular usefulness of members of this group as compensators for correction of frequency drift, lies not only in th possibility of obtention of both positive and negative temperature coefiicients of a wide variety, but also the possibility of controlling the degree of variation through choice or the proper composition. These properties, coupled with extremely low power factors in some cases, afford a high degree of usefulness for this latter class of application.

In general, the novel com ositions of the present invention comprise fired mixtures of the titanates and stannates of the alkaline earth metals. In a broad sense these mixtures may consist of one or more titanates with one or more stannates. While the alkaline earth metal compounds generally are of utility in the present invention, those of particular importance are the stannates and titanates of barium, strontium and calcium. In general the total stannate content of the ceramic body will not exceed 50%. The general classes of compositions covered by this invention are indicated in the examples. The peculiarly beneficial effect of the stannate additions is most strikingly shown in the case of such additions to barium titanate. At radio frequencies barium titanate has a dielectric constant of 1200-1300, and a temperature coeflicient which Not only may this erratic behavior be eliminated by addition of the stannates but dielectric constants at least as high as 13,000 at radio frequencies are possible.

In the practice of the invention the ingredients as indicated in the table below are properly reacted ceramically and then ground so that the coarsest particles will pas a 325 mesh screen. The dried powders are then mixed within the limits indicated by the proportions given in the table. Approximately 10% water is added and thoroughly mixed in and the damp powder granulated by passage through a 20 mesh screen. The granules are then pressed in a die under a pressure of 5 to 10 tons per square inch, and then allowed to air dry for 24 hours. The pieces used for purposes of test were roughly 1 inch in diameter and 0.1 inch thick. Pieces of such size were fired on a schedule of 400 F. per hour to the peak temperature, then held at peak temperature for three hours and then allowed to cool. The maturation temperature for all the bodies listed below is between 2450 and 2500" F. After cooling the opposing parallel surtaces are painted with silver powder paste which is fixed as a silver electrode by firing to 1500 I".

The values obtained below were determined at one megacycle using a radio frequency bridge of standard design. Resistivity was determined on a high sensitivity resistance circuit on which a resistance of a million megohms could easily be detected. the zero point indicator being a galvanorneter. The 1000 cycle measurements were obtained through use of an impedance bridge of standard design, whose arms were resistive components.

Having described the method of practice of the invention, the following sets of tables indicate the type of compositions and the values obtained thereon.

The peculiar advantage of such compositions as capacitor materials for by-pass and filter condensers may be seen from perusal of the followin: flames. For example, present day electrolytic condensers at best have power factors between 6.0% and 16.0% whereas all the values in the table are below 3.0%. Thus such materials may be used as substitutes for paper and electrolytics. Bodies having power factors below 0.1% are suitable as substitutes for mica capacitors. The possibility of variation and control of temperature coefllcients, thus making available these compositions as compensator compositions, is indicated from the data given in Table V and following. These temperature coeiflcients were measured at one megacycle.

Table I.--CaTtO; series One megacycle One kllocycle 553 P P 0. over ower Dielec. Dlelec.

constant W constant percent percent NIH-1 BaSnOn- 102 0. 010 171 1. 3 NIH- 3:81:01" 158 0. 010 165 l. 3 1111-1-10 BaSnOn. 148 0. 010 161 1.3 I) Ba8nO|.- 131 0. 010 139 1. 2 BaBn 142 0.015 149 1.3 no nssno.-. 133 0. 015 140 1. 4 1 1 BrBnO'--- 145 0. 010 155 1.4 1 5 8r8nO|-- 133 0. 010 148 1. 4 1 10 Brfln 132 0. 010 137 1. 4 I) STBnOe.-- 107 0. 010 123 1. 4 BlflllOa... 77 0.010 86 1.7 50 SrBnOa--. 57 0. 01!) 78 2. 5 1 1 CaBnO;.- 150 0.010 157 1.4 1 5 Cash 1.. 145 0. 010 153 1.3 1111-1-10 Oa8n0|. 132 0. 010 142 1. 4 I) C 01.- 103 0. 010 117 1. 4 CaSnO. 70 0. 010 86 2. 1 +50 (3081101.- 01 0. 010 72 1.8

Table II.-SrTiO.1 senes One megacycle One kilocycle 1?" m; P P

3:31:20 mm 53 5: MW

percent percent 1 1 Ba8nO| 249 0.010 1.1 1 5 BaSnOa 247 0. 010 240 1.0 1 10 13831101. 210 0.010 220 1. 7 81+!) BaBn0 233 0. 010 237 1. 2 05+35 1308110. 155 0.040 103 1. 9 50-1-50 Ba 0;. 99 0.030 97 1. 0 1lIH-1 811110;--. 242 0.040 244 1. 2 llIH-B BI'BI10|.- 227 0. 060 238 1. 2 NIH-l0 BrBnOi- 215 0. (B0 217 1. 2 ao+ao SlBnOs... 144 0. 010 149 1. 7 23x35 8r 0;. 70 0.010 84 2.0 50 BrBnO|.- 0. 030 52 8. 0 1i!) 1 CaSnOa" 247 0.030 201 1. 1 1 5 CaBnOa. 237 0.040 244 1.1 1 10 CaBnOr. Z3 0.0% 214 1.1 UH-N CaSnOa. 141 0. 010 146 1.3 35 Oa8nO;.- 07 0. 010 10s 2. 5 OaBnO..- 75 0.010 85 1. 5

Table III .--BaTiO1 series One megecyelc One kllocycle Grcqmp. BaTiOTStan- P M P 0 na 0 ow ower Dielcc. Dielec. factor, rm,

constant can constant w an 100+! BflB1l0l-- 1, 525 0. 820 1, 590 l. 0 100-1-5 11118110, 2, 010 1. 190 2,155 1. 0 100-H0 B11811 3,580 2. 730 3,970 1. 4 80-1-21 B38110. 4,175 0. 870 4, 275 0. 0] 05-1-35 BaSnOL 079 0.420 683 0.03 50-1-50 BaSnOi. 263 0. 2% 280 2. 5 100+] SIBHO l, 050 0.950 1, T30 11 100-1-5 SrBnO;. 2, 300 1. 500 2, 470 i. 8 100-1-10 SrSnOp. 4. 300 0. 980 4, 780 2. 4 80+!) SrSnOa. 1, 720 0.320 1, 735 0. 01 -1-35 SrSnOg. 593 0. Z10 605 0. 00 50-1-50 SrSnO;... 272 0. 180 270 1. 5 1001-1 0531101-. 1. 710 1.100 1,790 1.4 100-1-5 CaSnOL 2, 080 2. 000 2, 840 1. 8 100+10 CaSnO; 8, 500 2. 500 9, 400 1. 5 so+2o 0851101- 1. 420 0. 320 1, 445 0.02 05-1-35 CaSn0 235 0. 060 238 1. 1 50-1-50 CaSn0; 124 0. 010 130 1. 4 92-1-8 BaSnO.1 2, 810 2. 620 3, 200 2. 0 88-1-12 BaSnO; 6, 575 2. 720 7, 060 l. 2 21... 86-1-14 BaBnOg. 9, 450 2, 900 10, 200 0. 8 22 84-1-10 BaSnO; 12, 000 2. 200 13,100 0. 4 23... 82-1-18 B88110 15$ 1.000 7,250 0.1

Table IV.C'omple:r senes One megacycle One kilocycle Comp.

No. (mmlmmm Dlelec. 3g; Dielec. ,3, mm con- I cent cent 1 Ba'liO: 10 1355110... 4, 0.95 3, 510 0.01

10 SrBnO. 788218110; 20 1358110 1,44!) 0. 38 1, 415 0.01

1' 11 70 BaTiO; 10 BaSn0 2, 0-50 1, 0-02 21 SI'SnO 70 BaTiOa 15 BaSn0|.-.- 1,475 0. 31 1.450 0.10 15 BrSnO 85 BaTiO; 5 Ba8n0 7,731 1.74 8,111) 0. 50

5 SrSnO, 5 SrTiOe 70 BaTiO; 10 Bl8110s.-.- 1, 350 0. 23 1, 81) 0. D 10 BrSnOe 10 BrTlOa T10; 15 BaSn0; 615 0. 15 025 1. I1

15 SrBnOi 15 BrTi0 Table V.--Temperature capacity data Bod #3, Bed '0, Bot] '15, Temperature, C. 0.11 10. Ce'I iOi C6110 series series eerie! K K K 148 137 132 148 137 132 148 135 151 147 151 140 13) 134 m 134 13 144 133 13 143 132 12'! 141 131 I 140 129 125 139 128 124 138 127 us 137 1 1B Table VI.Temperature capacity data Bod Bod i0, Bod 415,

Temperature, C. Br 0; Br'I iO; Sr'fi series eerie! K K K 210 215 II 210 215 II 213 215 N7 201 213 I! 205 212 me 203 210 III 201 I! an: 1 110 1 105 ms 107 103 214 194 189 I72 101 180 200 I 184 ID 154 180 105 152 Table VII.Tempemture capacity series Bodyfi, Body #9, Body #15, Body #5, Temperature, 'C. BaiflO; Ba'lfiO BaTiO: Complex series series series series 3, 580 4, ill) 8, 500 7, 720

The temperature coefficients of the compositions covered in Tables V, VI and VII are indicative of the scope of variation possible. While single compositions may yield the desired coefficient, an infinite variety of coeilicient is possible through parallel combination of one or more bodies.

From the foregoing it will be seen that the present inventionprovides compositions eminent- 1y suitable as dielectric materials in a wide variety of uses. The above examples have been set forth as illustrative oi the invention, the scope thereof being comprehended within the appended claims as it will be apparent that wide variation may be had from the specific examples.

What is claimed is:

1. A ceramic composition which comprises the titanates and stannates of the alkaline earth metals.

2. A ceramic composition which comprises the titanates and stannates of the alkaline earth metals wherein the titanates are present in greater proportion than the stannates.

3. A ceramic composition which comprises a titanate of, an alkaline earth metal and a stannate of an alkaline earth metal.

4. A ceramic composition which comprises barium titanate and an alkaline earth stannate.

5. A ceramic composition which comprises barium titanate and calcium stannate.

6. A ceramic composition which comprises barium titanate and strontium stannate.

7. A ceramic composition which comprises barium titanate and barium stannate.

EUGENE WAINER. 

